Method and device for generating ultra-high pressure

ABSTRACT

A pressure source material is loaded into a space having constraint device  1 , which is formed partly by optically transparent material  1   a   , 1   b , and is disrupted under volume constraint. Light energy is externally supplied to the pressure source material constrained in the space through the optically transparent material by employing the device to apply light energy. The disruption of atomic bonds in the pressure source material is induced by heating the pressure source material above the boiling point thereof through the supplied energy. Exceptionally high pressures are generated in the space by the use of expansive forces arising from the disruption of atomic bonds. Such a configuration can implement ultrahigh pressure abilities that has not been achieved, so far.

The present application is a continuation-in-part of U.S. applicationSer. No. 10/284,477, filed Oct. 31, 2002, now U.S. Pat. No. 7,332,727,issued Feb. 19, 2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and device for generatingultrahigh-pressure, and more particularly to a method and device whichenables the generation of ultrahigh pressure in a space partlysurrounded by an optically transparent material with supplying lightenergy to the space externally.

2. Description of the Related Art

Although belt apparatus, multi-anvil apparatus and so on which enablethe syntheses of diamond and cubic boron nitride have generally beenused for the production of high pressure, high pressures above 10 GPa isdifficult to achieve by using these apparatuses. The apparatuses canproduce static high pressures and the sample volume can be enlarged upto 200 cm³. However, it is quite impossible to achieve high pressures inexcess of 100 GPa in these apparatuses. High pressures in the 100-GParegion can be attained only with diamond anvil cells or dynamic methods.

However, the sample volume attainable in diamond anvil cells is not muchlarger than 10⁻⁹ cm³ at pressures above 100 GPa. Large-scale apparatusesare needed for ultrahigh pressure experiments using high explosives orgas guns which have generally been used in dynamic methods. The shockduration is extremely short and limited to a few microseconds.Furthermore, it has not been reported until now that ultrahigh pressuresabove 1 TPa are generated by these dynamic methods. The generation ofultrahigh pressure beyond 1 TPa has been achieved only in impactexperiments using nuclear explosion or high-power lasers developed forthe purpose of nuclear fusion. However, the duration of generatedultrahigh pressure cannot exceed a few nanoseconds.

Since the sample volume of diamond anvil cells is extremely small, thediamond anvil cell is impossible to use in industrial production.Furthermore, the production of ultrahigh pressures in excess of 1 TPausing diamond-cell technique cannot be expected. In the conventionaldynamic methods, the duration of the high-pressure generation isextremely short. The applications of the dynamic methods to syntheses ofmaterials via phase transformation are limited to irreversibly formedmetastable phases. Thus, the conventional dynamic methods haveapplication only in the extremely limited region.

SUMMARY OF THE INVENTION

In view of the above-described impasse, a main object of the inventionis to provide a method and device for generating ultra-high pressurethat have not been achieved in the conventional methods, so far.

Another object of the invention is to provide a method and device forgenerating ultra-high pressure with considerably longer durationcompared to the conventional dynamic methods.

Still another object of the invention is to provide a method and devicefor generating ultra-high pressure in extremely larger sample chambercompared to the diamond anvil cells.

Yet another object of the invention is to provide a method and devicefor generating ultra-high pressure with the supply of energy some ordersof magnitudes less than those in the conventional dynamic methods.

A further object of the invention is to provide a method and device forgenerating ultra-high pressure in which high temperature and highpressure required for syntheses can be simultaneously produced in thesample chamber and the high temperature can be controlled separately.

In accordance with the present invention, there is provided a method forgenerating ultra-high pressure comprising the steps of:

loading a pressure source material under volume constraint in a spacepartly surrounded by an optically transparent material, the ultra-highpressure source material being expanded in volume through disruption ofits atomic bonds;

disrupting the atomic bonds by heating the pressure source materialabove the boiling point thereof using optical energy externally suppliedto the pressure source material through the optically transparentmaterial; and

generating ultra-high pressure within the space using expansive force ofthe high pressure inducing material arising from the disruption ofatomic bonds.

In the method described above, a pressure source material expanded dueto the breaking of its atomic bonds is packed in a space partlysurrounded by optically transparent material and light energy isexternally supplied to the pressure source material through theoptically transparent material to disrupt its atomic bonds by heatingthe pressure source material above the boiling point thereof undervolume constraint. Therefore, since ultrahigh pressures are generated byexpansive forces arising from the disruption of atomic bonds in thepressure source material, if only a relatively small light energy enoughto induce the disruption of atomic bonds is supplied to the pressuresource material, ultrahigh pressures can be generated. Furthermore,pressures generated in the volume-constrained space are exceptionallyhigh because expansive forces occurring from the pressure sourcematerial disrupted against its very strong bonding forces are extremelylarge.

In a preferred embodiment, the pressure source material is irradiatedwith pulsed laser light through the optically transparent material tosupply the light energy.

Since the supply of light energy is made by the irradiation of pulsedlaser light through the optically transparent material, the light energycan be efficiently supplied to the pressure source material and wellcontrolled by changing the intensity and the duration of pulsed laserfrom the existing pulsed laser equipment which can emit laser lightshaving a wavelength suitable for heating the pressure source materialabove the boiling point thereof.

In a preferred embodiment, the optically transparent material is hightransmittance to the pulsed laser light.

Since the optically transparent material has high transmittance for thepulse laser light, the externally supplied light energy can pass theoptically transparent material without raising its temperature due toenergy absorption and thermal stresses causing damage to the opticallytransparent material can hardly occur.

In a preferred embodiment, the optically transparent material issapphire.

Since sapphire has high transmittance compared with diamond and a largesingle crystal of synthetic sapphire is available at a low price, it issuitable for the optically transparent material forming the space inwhich high pressures are generated.

In a preferred embodiment, the pressure source material is made of asimple substance having a large absorption coefficient and strong atomicbonds, or a compound substance which is a mixture of materials havingthe large absorption coefficient and/or the strong atomic bonds toprovide the large absorption coefficient and strong atomic bonds as awhole.

Since the pressure source material is a substance having largeabsorption coefficient and strong atomic bonds, considerably largeexpansive forces can occur if only a relatively small energy is suppliedto the pressure source material. Furthermore, since the pressure sourcematerial is a mixture of materials, which has large adsorptioncoefficient or strong bonds, possessing large absorption coefficient andstrong atomic bonds as a whole, the generated pressure and its durationcan be controlled by combining materials.

In a preferred embodiment, the type of the atomic bonds is a covalentbond, a metallic bond or a hydrogen bond.

The pressure source material can be chosen among materials which havecovalent, metallic, and hydrogen bonds according to need. Therefore,temperature of the pressurized and heated sample can be controlledbecause temperature gradients across the pressure source material can bechanged by combining materials that have different light absorptioncoefficients or various types of atomic bonds.

In a preferred embodiment, the simple substance is graphite.

Since graphite has not only large light absorption coefficient but alsostrong covalent bonds, graphite can be singly used as the pressuresource material and furthermore the use of graphite as pressure sourcematerial enables the generation of ultrahigh pressure with high energyefficiency.

In a preferred embodiment, the compound substance is a mixture ofpowdered graphite and water.

Since hydrogen bonds or atomic bonds in water are disrupted by heatoccurring in graphite which absorbs light energy, large expansion ofwater takes place. Therefore, the maximum pressure generated in themixture of graphite and water can be higher than that in individualgraphite.

In a preferred embodiment, the pressure source material is irradiatedwith a pulsed laser beam through the optically transparent material insuch a manner that the pulsed laser beam has a beam spot having adiameter adjusted to that of the pressure source material so that thepulsed laser light provides a minimum diameter not within the opticallytransparent material.

The pulsed laser beam is condensed on the pressure source materialthrough the optically transparent material so that the minimum diameterof the laser beam is not formed within the optically transparentmaterial. Therefore, as the position where the intensity of pulsed laserbeam is highest does not exist in the inside of the opticallytransparent material, the local temperature increase in the opticallytransparent material can be avoided.

In accordance with this invention, there is provided a method forgenerating ultra-high pressure comprising the steps of:

loading at least graphite as a pressure source material under volumeconstraint in a space surrounded by optically transparent sapphireanvils;

disrupting the atomic bonds of the graphite by irradiating the graphiteunder volume constraint with pulsed laser light externally through thesapphire anvils to heat the pressure source material above the boilingpoint thereof; and

generating ultra-high pressure within the space using force arising fromthe disruption of atomic bonds.

Since graphite is at least loaded under volume constraint into a spacepartly surrounded by optically transparent material and the graphite isdisrupted by heating the graphite above the boiling point thereof withlight energy supplied externally through the optically transparentmaterial and thereby ultrahigh pressures are generated in the space bythe use of expansive forces arising from the disruption of covalentbonds in graphite, the supplied light energy is efficiently absorbed inthe graphite, which is quickly heated up to a high temperature requiredto disrupt the atomic covalent bonds in graphite and exceptionally highpressure can accordingly be achieved with a relatively small lightenergy because very large expansive forces occur in the graphitedisrupted against its very strong covalent bonds.

In accordance with the invention, there is provided a device forgenerating ultra-high pressure comprising:

loading means for loading a pressure source material under volumeconstraint in a space partly surrounded by an optically transparentmaterial, the ultra-high pressure source material being expanded involume through disruption of its atomic bonds; and

light energy supplying means for externally supplying optical energy tothe pressure source material through the optically transparent material,wherein the pressure source material is heated above the boiling pointthereof by the light energy externally supplied by the light energysupplying means so that the atomic bonds are disrupted, and ultra-highpressure is generated within the space using expansive force of the highpressure inducing material arising from the disruption of atomic bonds.

In the device described just above, a pressure source material is packedunder volume constraint in a space partly surrounded by opticallytransparent material which is equipped with the device to constrainexpansion. By means of the device to supply light energy, light energyis externally supplied to the pressure source material under volumeconstraint through optically transparent material to disrupt its atomicbonds by heating the pressure source material above the boiling pointthereof and ultrahigh pressures are generated in the space by expansiveforces arising from the disruption of atomic bonds in the pressuresource material. Therefore, ultrahigh pressures can be generated by arelatively small light energy enough to induce the disruption of atomicbonds by heating the pressure source material above the boiling point.Furthermore, pressures generated in the volume-constrained space areexceptionally high because expansive forces occurring from the pressuresource material disrupted against its very strong bonding forces areextremely large.

In a preferred embodiment of the device, the means for supplying lightenergy is equipped with a pulse laser that emits a pulsed laser beamapplied to the pressure source material through the opticallytransparent material.

In this configuration, light energy can be efficiently supplied to thepressure source material through the optically transparent material bycontrolling the intensity and the duration of the pulsed laser using theexisting pulsed laser equipment that can emit laser beam having asuitable wavelength for heating the pressure source material above theboiling point thereof.

In a preferred embodiment of the device, the light energy supplyingmeans has an optical adjusting system for adjusting the diameter of thelaser beam so that the pulsed laser beam provides a minimum diameter notwithin the optically transparent material before the pulsed laser beampenetrates the optically transparent material. Since by using the deviceto supply light energy to the pressure source material, the pulsed laserbeam can be condensed on the pressure source material through theoptically transparent material so that the minimum diameter of the laserbeam is not formed within the laser-irradiated optically transparentmaterial and the spot diameter at the pressure source material can bedetermined, the position where the intensity of pulsed laser beam ishighest, does not exist in the inside of the optically transparentmaterial and thereby the local temperature increase in the opticallytransparent material can be avoided.

In a preferred embodiment of the device, the light energy supplyingmeans has an optical splitting means for splitting the pulsed laser beaminto plural parts to be applied to the high pressure source materialconstrained in the space from plural directions.

In this configuration, the laser beam is divided into some ones and thedivided laser beams are separately applied to the pressure sourcematerial constrained in the space from some different directions.Therefore, as larger expansion occurs in the space compared to the caseof irradiating in one direction, higher pressure can be achieved.

In an preferred embodiment of the device, a radiative transitionmaterial is loaded together with the high pressure source material inthe space, the radiative transition material emitting fluorescenceexcited by laser and changing its wavelength according to pressurewithin the space, and the device further comprises:

a wavelength measuring means for measuring the wavelength of thefluorescence emitted by the radiative transition material; and

a pressure estimating means for estimating the ultra-high pressuregenerated within the space from shifts in wavelength of the fluorescenceemitted from the radiative transition material.

Since the pressure sensor which changes the wavelength of fluorescenceemission dependently on pressure is loaded into the space together withthe pressure source material, high pressures generated in the space canbe measured on the basis of the observed wavelength of the fluorescencefrom the pressure sensor using the optical system. Therefore, how thegenerated pressure changes by the use of various pressure sourcematerials or by the way of supplying light energy, can be investigated.

In a preferred embodiment, the device further comprises:

means for measuring the temperatures of the space, wherein spectra ofthermal radiations from the space are observed during disruption of thepressure source material and the temperatures are obtained from theobserved spectra.

Since spectra of thermal radiations from the space during the disruptionof the pressure source material can be observed and temperatures in thespace can be estimated from the observed spectra, how the temperature ofthe space changes during the disruption of atomic bonds by the use ofvarious pressure source materials or by the way of supplying lightenergy, can be investigated.

The above and other objects and features of the invention will be moreapparent from the following description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an embodiment of a ultra-highpressure device generating ultrahigh pressures employing the ultra-highpressure method based on the present invention;

FIG. 2 is a sectional side view showing the high-pressure device 1 inFIG. 1;

FIG. 3 is a diagram illustrating the methods to measure ultrahighpressure and ultrahigh temperature generated by the use of the presentinvention;

FIG. 4 is a graph showing the form of pulsed laser emitted from thepulsed laser equipment in FIG. 1;

FIGS. 5A and 5B are CCD camera records of pulsed laser applied to thepressure source material and the pressure shifts of ruby fluorescencelines, which were measured during the ultrahigh pressure experiment inwhich graphite is used as pressure source material;

FIGS. 6A and 6B are CCD camera records of pulsed laser applied to thepressure source material and the pressure shifts of ruby fluorescencelines, which were measured during the ultrahigh pressure experimentwhere a mixture of powdered graphite and water is used as the pressuresource material;

FIG. 6C shows a temperature of a boundary between the pressure sourcematerial and a sapphire anvil;

FIG. 7 is a schematic view showing other embodiment of a ultra-highpressure device generating ultrahigh pressures by the use of the presentinvention; and

FIG. 8 is a sectional side view showing the high-pressure device 1 inFIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the accompanied drawings showing an embodiment of theinvention, the present invention will be explained

FIG. 1 is a schematic drawing showing an embodiment of the device basedon the ultra-high pressure method according to the present invention. InFIG. 1, the ultra-high pressure device has a space partly surrounded byoptically transparent material where a pressure source material isloaded and its atomic bonds are disrupted under volume constraint byheating the pressure source material above the boiling point thereof,and in which a high-pressure device 1 to constrain expansion of thepressure source material is installed.

The high-pressure device 1 will be explained in detail referring to FIG.2. As shown in FIG. 2, the high-pressure device consists of a pair ofsapphire anvils 1 a, 1 b having high transmittance and gasket 1 c havinga hole which form a space 1′ where the pressure source material 2 isloaded, and a screw-clamped anvil cell (not illustrated) which holds thesapphire anvils and presses the gasket 1 c between the flat parallelfaces of the sapphire anvils.

The gasket 1 c illustrated in FIG. 2 is held between the pressure facesof a pair of sapphire anvils so that the pressure source material iscompressed to 5 GPa. As shown in FIG. 2, a part of the gasket 1 csandwiched between the sapphire anvils is crushed and thecircumferential region of this part rises. The gasket shown as anexample was Cu—Be foil of 0.2 mm thickness with a hole (0.15 mm indiameter) before compressing it by sapphire anvil cell. The volume ofthe space 1′ is 3.53×10⁻³ mm³. A foil of soft metal such as Cu—Be or Cuis usually used as gasket for sapphire anvil because such soft metaldoes not damage the pressure face of sapphire anvil.

The ultra-high pressure apparatus is equipped with a device to applylight energy which generates light energy to externally supply lightenergy to the pressure source material constrained in the space 1′ ofthe high-pressure device 1 through a pair of sapphire anvils 1 a, 1 b.The device has a pulsed laser equipment 3 a that generates pulsed laserlight supplied to the pressure source material through a pair ofsapphire anvils 1 a, 1 b. For example YAG laser is used as the pulsedlaser 3 a. In this embodiment, the pulsed YAG laser using slab typeNd:YAG crystal was chosen, which can generate high power laser with agood beam quality. In this pulsed laser equipment, the peak power andthe duration of pulsed laser can be changed arbitrarily.

The device to apply light energy has two mirrors 3 b 1, 3 b 2 whichreverse the direction of laser light from pulsed laser 3 a. A laserlight from the pulsed laser 3 a is reflected from mirror 3 b 1 so thatit changes its direction at right angles, and the laser light reflectedfrom mirror 3 b 1 changes its direction at right by mirror 3 b 2 again.

Owing to the use of slab type Nd:YAG crystal, the spot of laser beamfrom the pulsed laser 3 a has a rectangular shape and the rectangularspot becomes to be elongated as the position is apart from an exit ofthe pulsed laser 3 a because of difference in spreading between widthand length. In order to prevent the beam expansion and the elongation ofbeam spot, a circular aperture is placed in the resonator of the pulsedlaser 3 a and furthermore pupil transfer lens 3 c 1 and 3 c 2 are putbetween pulsed laser 3 a and mirror 3 b 1 and between pulsed laser 3 aand mirror 3 b 2, respectively. Thus, in order to use the output powerof the pulsed laser effectively, said device is devised to obtain beamspot as circular as possible. By means of the device to apply lightenergy, laser light from mirror 3 b 1 is reflected by mirror 3 b 2 andthe reflected laser light is applied to the pressure source materialconstrained in the space of the high-pressure device 1 through sapphireanvil 1 a and the size of the beam spot at the pressure source materialis adjusted so that the minimum diameter of the laser beam is not formedwithin sapphire anvil 1 a. The size of the laser spot is determined bychanging the positions of lens 3 d 1 after adjusting the focus ofobjective lens 3 d 2. The position and the size of beam spot are decidedusing monitor system 3 e. When the position and the size of beam spotare adjusted observing the pulsed laser spot, a dimming filter (notillustrated) is put in laser light paths.

After the focus of objective lens 3 d 2 is adjusted to the interfacebetween sapphire anvil 1 a and pressure source material 2, the positionsof lens 3 d 1 are controlled so that the size of laser beam spot at theinterface between sapphire anvil 1 a and pressure source material 2coincides with that of the end of pressure source material 2.

In the monitor system 3 e, lights from a source of illumination 3 e 1are reflected by beam splitter 3 e 2 and the reflected lights areapplied to the interface between sapphire anvil 1 a and pressure sourcematerial 2 through objective lens 3 d 2. The interface is taken with CCDcamera 3 e 4 through objective lens 3 d 2 and beam splitter 3 e 2, 3 e3, which is projected on the monitor 3 e 5. The focus of objective lens3 d 2 is adjusted to the interface while observing the picture of theinterface projected on the monitor 3 e 5 so that a clear picture can beprojected.

As described above, the size of laser spot at the interfaceapproximately agrees with that of the end of pressure source material 2when the objective lens 3 d 2 is focused. When a trial pulsed laserlight of low intensity emitted from pulsed laser 3 a is applied to thepressure source material 2 through the dimming filter, the spot of thelaser light at the interface can be observed by monitor 3 e 5. Therebyit can be confirmed whether the size of laser spot at the interfaceapproximately agrees with that of the end of pressure source material 2or not. After that, beam splitters 3 e 2 and 3 e 3 in the monitor system3 e are removed from the laser light paths as indicated by arrows inFIG. 1.

As described above, after the position and the size of beam spot aredecided using monitor 3 e, beam splitters 3 e 2 and 3 e 3 in the monitorsystem 3 e are removed from the laser light paths and subsequently alaser beam having the predetermined energy and duration is emitted fromthe pulsed laser 3 a. The pressure source material 2 which is loadedunder volume constraint in the space 1′, is irradiated with the laserbeam through pupil transfer lens 3 c 1, mirror 3 b 1, pupil transferlens 3 c 2, mirror 3 b 2, lens 3 d 1, objective lens 3 d 2, and sapphireanvil 1 a. The pressure source material 2 is heated with the irradiationof the pulsed laser, which is disrupted by heating the pressure sourcematerial above the boiling point thereof and expanded due to thedisruption. Since the expansive forces arising from the disruption ofatomic bonds are very large, ultrahigh pressures are generated in thespace 1′.

The ultra-high pressure device shown in FIG. 1 is also equipped with apressure-measurement system for measuring ultrahigh pressures generatedin the space 1′ and a temperature-measurement system for observingtemperatures in the space 1′ based on thermal radiations from the space1′ during the disruption of the pressure source material. Before theexplanation of the pressure and temperature measurement systems, theprinciples of the present pressure and temperature measurements will beexplained referring to FIG. 3.

As shown in FIG. 3, a ruby 4 a used as pressure sensor is loaded in theplace 1′ together with the pressure source material 2 so that it isplaced near the interface between the pressure source material 2 and thesapphire anvil 1 b opposite to the sapphire anvil 1 a through whichpulsed laser beam B passes. The pressure source material is disrupted byheating above the boiling point thereof through the irradiation ofpulsed laser. The expansive forces resulting from the disruption istransmitted in the pressure source material 2 packed in the space 1′ andis exerted on the ruby 4 a, in which ultrahigh pressures are generated.

Fluorescence emission (B11) from the ruby 4 a is excited by theirradiation of laser beams B1 through sapphire anvil 1 b. Since thewavelength of the fluorescence depends on pressure exerted on the ruby 4a in the space 1′, ultrahigh pressure generated in the space 1′ can beestimated by measuring the wavelength of fluorescence B11 from the ruby4 a.

When the ruby is not irradiated with the excitation laser beam B1through sapphire anvil 1 b, spectra of thermal radiations emittedthrough the sapphire anvil 1 b from the space 1′ are observed at theinterface between sapphire anvil 1 b and pressure source material 2. Inorder to eliminate influences of the optical system which the radiantlights pass, a spectrum of radiation from the standard light source ismeasured by using the optical system. The spectra of thermal radiationfrom the space 1′ are corrected on the basis of this result. Thustemperatures at the interface in the space 1′ can be measured.

Returning to FIG. 1, an explanation of the pressure and temperaturemeasurement systems follows. The objective lens 4 b to irradiate theruby 4 a with excitation laser beam B1 and the monitor system 4 c toadjust the focus of the objective lens 4 b are installed in the system.

The monitor system 4 c has the same configuration as the monitor system3 e. In the monitor system 4 c, lights from the illumination-lightsource are reflected by beam splitter 4 c 2, the reflected lights areapplied to the interface between sapphire anvil 1 b and pressure sourcematerial 2 through objective lens 4 b. The interface is taken with CCDcamera 4 c 4 through objective lens 4 b and beam splitter 4 c 2, 4 c 3,which is projected on the monitor 4 c 5. The focus of objective lens 4 bis adjusted to the interface while observing the picture of theinterface projected on the monitor 4 c 5 so that a clear picture can beprojected on the monitor 4 c 5.

After the focus of objective lens 4 b is adjusted to the interface, beamsplitters 4 c 2 and 4 c 3 in the monitor system 4 c are removed from thelaser light paths as indicated by arrows in FIG. 1. At the pressuremeasurement, beam splitters 4 c 2 and 4 c 3 in the monitor system 4 care removed from the laser light paths. The laser beams from the argonlaser to excite fluorescence emissions form ruby are reflected by beamsplitter (not illustrated) and the reflected laser beams are applied tothe ruby 4 a in the space 1′ through objective lens 4 b so that the ruby4 a emits the fluorescence B11. The fluorescence from the ruby 4 apasses beam splitter (not illustrated) and reaches the monochromator(not illustrated) where the ruby fluorescence lights are dispersed.

At the temperature measurement, radiant lights from the interfacebetween the sapphire anvil 1 b and the sample are made parallel byobjective lens 4 b and are transmitted to the monochromator (notillustrated). The observed spectra of radiation from the space 1′ arecorrected. The temperatures at the interface in the space whereultrahigh pressure is generated, are obtained on the basis of thecorrected spectra. Here, 4 d is a notch filter for YAG-laser wavelengthwhich cut off only the YAG laser light so that the pulsed laser lightcould not reach the optical system for measuring temperature andpressure to damage it.

By the use of the ultra-high pressure apparatus described above,powdered graphite is loaded into the space 1′, which is formed by a pairof sapphire anvils 1 a, 1 b, and gasket 1 c, together with ruby 4 aunder volume constraint. As shown in FIG. 4, the powdered graphite isheated with the irradiation of 0.5 ms-duration pulsed laser having awavelength of 1060 nm emitted from the YAG pulse laser equipment throughone sapphire anvil 1 a. The atomic covalent bonds in graphite aredisrupted by heating above the boiling point thereof. Then fluorescenceemission from the ruby 4 a was dispersed by the monochromator and thechange in wavelength of the fluorescence was recorded in a cooled CCDcamera. The recorded time-resolved ruby fluorescence is shown in FIG. 5(b). As seen from the pressure scale which is estimated from thewavelength scale, ultrahigh pressures in the 400-500 GPa region areachieved in the space 1′ of the high pressure device 1 with the durationof about 0.5 ms because of the disruption of atomic covalent bonds ingraphite. The amount of energy supplied to the pressure source materialby pulse laser equipment 3 a is estimated to be 0.25 J, which isconverted into the energy per unit area and unit time of 3.5×10⁶ W/cm².FIG. 5( a) shows the wavelength and the duration of pulsed laser. Thepressure scale in FIG. 5( b) is obtained based on the well knownrelation between pressure p [TPa] and the shift Δλ [nm] in thewavelength of R₁ ruby fluorescence: p=0.3808[(Δλ/694.2+1)⁵−1].

A small quantity of water was dropped into powdered graphite and thismixture of powdered graphite and water was kneaded together. When themixture of powdered graphite and water was loaded into the space 1′ aspressure source material, an ultrahigh-pressure experiment was madeunder the same condition as in the above experiment where only graphitewas used as pressure source material. The result is shown in FIG. 6. Asseen from the result, ultrahigh pressures in excess of 1 TPa aregenerated for approximately 0.2 ms because of the disruption of atomiccovalent bonds in graphite and hydrogen bonds in water. It is evident oncomparing the result in FIG. 5 with that in FIG. 6 that the generationof ultrahigh pressures above 1 TPa may originate from the disruption ofhydrogen bonds or covalent bonds in a large quantity of water ratherthan that of covalent bonds in graphite.

High temperature of the irradiated part of the pressure source materialwas net measured in the experiment described above. FIG. 6C shows thetemperature of the irradiated part of the pressure source material, thatis, a boundary between the pressure source material and the sapphireanvil. The temperature reached to about 9200° C. The temperature insidethe pressure source material reaches higher than 9200° C. It is apparentthat the temperature of the pressure source material is above theboiling point (about 5000° C.) thereof. It is clear from the result ofthe experiment that the maximum pressure can be increased to a pressureof 1 TPa or above it with increasing the intensity of the pulsed laseror extending the duration of pulsed laser without changing the peakintensity.

By using the optical system which consists of lens 3 d 1 and objectivelens 3 d 2, the spot diameter of pulsed laser beam at the interfacebetween the pressure source material and sapphire anvil is adjusted tothe size of the end of pressure source material 2 so that the minimumdiameter of the laser beam is not formed within the sapphire anvil 1 a.Thereby the minimum diameter of the pulsed laser that enables thedisruption of atomic bonds in the pressure source material by heatingabove the boiling point thereof, cannot exist within sapphire anvil 1 ain which the laser beams passes. Therefore, even if the output power ofthe laser beam from the pulsed laser equipment 3 a is increased to someextent, the damage of the sapphire anvil 1 a due to thermal stressresulting from the local temperature increase can be avoided. Thus asgreater pulsed laser can be applied to the pressure source material inthe space 1′ with longer duration, higher pressure can be generated andthese can also be maintained for a longer time.

A simple substance such as graphite having large absorption coefficientand strong atomic bonds, or a compound substance having a largeabsorption coefficient and strong atomic bonds as a whole, which is amixture of materials such as graphite, metals, water, etc. having alarge adsorption coefficient or strong bonds, can be used as thepressure source material loaded into the space 1′ which is formed by apair of sapphire anvils 1 a, 1 b and gasket 1 c. In order to pack thepressure source material into the space 1′ easily, the materials used aspressure source material are crushed into powder.

When the pressure source material has larger absorption coefficient, itcan be heated up to higher temperature with smaller light energy becauseit absorbs the externally supplied light energy with high efficiency.When the pressure source material has stronger atomic bonds, higherpressures can be generated in the space 1′ because lager expansiveforces can be obtained from the disruption of the atomic bonds.

The pressure source material is constrained in the space partly formedby sapphire anvils 1 a, 1 b in which the light energy externallysupplied to the pressure source material passes. Sapphire has not onlystrength enough to sustain the ultrahigh pressure generated in the spacebut also very high transmittance. Since sapphire does not absorb almostall the light energy passing it, the temperature of sapphire anvil doesnot rise very much. The sapphire anvil is hard to be damaged due to thepassing of light energy. By the way, the following relations isestablished: I=I₀e^(−ad) (I: intensity of ejective light, I₀: intensityof incident light, a: light absorption coefficient, d: thickness). Thelight absorption coefficient estimated for a typical type-IA diamond,which can be considered to be favorable with respect to thetransmittance, is 6.5 cm⁻¹ from the above relation, whereas that forsapphire anvil is 0.28 cm⁻¹, which is considerably small compared withtype-IA diamonds. Since a large single crystal of synthetic sapphire isavailable, a larger pressure chamber can be formed with sapphire anvils.Furthermore, sapphire anvils can maintain the pressure source material 2at high temperature so that heat cannot escape from the pressure sourcematerial 2 to the outside, for a considerably long time compared todiamond anvils, because sapphire has much lower thermal conductivitythan diamond. Thus, the sapphire anvil is suitable for maintainingultrahigh pressures generated in the pressure chamber for longer time.

In the embodiment described above, the space 1′ in the high-pressuredevice is formed by sandwiching a metal foil with a hole betweenopposite sapphire anvils, which has the most simple opposed anvil cell.By the use of anvils more than three, larger pressure chamber can beformed and furthermore the use of the multi-anvil cell enables theirradiation of pulsed laser not only from one direction but also fromsome different directions. Thereby higher pressures can be expected tobe achieved in the large space.

A simple device using opposed anvil cells in which pulsed laser lightsare applied to the pressure source material through both of two opposedanvils can be proposed as shown in FIG. 7. Here, a laser beam emittedfrom the pulsed laser equipment 3 a is divided into two beams by thebeam splitter 10 a where one beam goes straight on and another beam isreflected from the beam splitter. The beam which goes straight on isapplied to the pressure source material through objective lens 3 d 2 andsapphire anvil 1 a in the same way as that shown in FIG. 1. On the otherhand, the reflected beam is led to beam splitter 10 c through pupiltransfer lens 10 b and is reflected from the beam splitter 10 c so thatit changes its direction at right angles. The reflected beam from 10 cis applied to the pressure source material through sapphire anvil 1 b.Thus, the light energy is supplied to the space 1′ of the high-pressuredevice 1 from two opposed directions. Therefore, ultrahigh pressuresmore than two times those in the configuration as shown in FIG. 1 can beachieved in the central portion of the pressure chamber.

In the embodiment as demonstrated in FIG. 7, two same devices to applypulsed laser to the pressure source material as that in theconfiguration shown in FIG. 1 are equipped in symmetry on both sides ofthe sapphire anvil cell 1, where objective lens 11, lens 12, monitorsystem 13 correspond to 3 d 2, 3 d 1, and 3 e on the side of sapphireanvil 1 a in FIG. 1, respectively.

Two beam splitters in the monitor system 13 are removed from the laserlight paths after the position and the size of beam spot are decidedusing the monitor system 13, in the same manner as in the case ofmonitor system 3 e. When measurements of pressure and temperature aremade, lens 11, objective lens 12, and monitor system 13 are removed fromthe laser light paths together with beam splitters 10 a and 10 b andsubsequently objective lens 4 b is returned to the original position.

According to the embodiment described above, the present invention notonly enables the generation of ultrahigh pressure above 1 TPa but alsoincreases the duration of ultrahigh pressure generation by approximately10⁴ times compared to the conventional methods. Furthermore, the outputof pulsed laser required to generate the ultrahigh pressures is someorders of magnitude less than in the conventional methods. The presenthigh-pressure device can be embodied in considerably small scalecompared to the conventional dynamic methods which enable the generationof pressures in the 1-TPa region. In addition, when sapphire anvils areused for constraining expansion of the pressure source material, thepressure chamber having a volume of some cubic millimeters can beestablished. Thus the ultra-high pressure device based on the presentinvention has ultrahigh-pressure ability that cannot be achieved bymeans of any other existing high-pressure methods. The possibilities fordiscoveries and syntheses of new materials with novel physical andchemical properties are far increased by employing this device.Furthermore, if diamond anvils harder than sapphire are used for volumeconstraint, ultrahigh pressures several orders of magnitude higher than1 TPa are probably achieved by further development in the presenttechnique.

In the present invention, an ultrahigh-pressure method and the deviceare proposed, in which a matter constrained by optically transparentmaterials is disrupted by heating the matter above the boiling pointthereof with the irradiation of pulsed laser light through the opticallytransparent material and ultrahigh pressures above 1 TPa can be achievedby constraining expansion due to the disruption. The duration of theultrahigh pressure generation is longer by more than four orders ofmagnitude than those in the high-pressure experiments using laser-drivenshock wave which can generate ultrahigh pressures above 1 TPa and isalso longer by more than three orders of magnitude than that in theshock wave method using a two-stage gas gun which can generate severalhundred gigapascals. The sample volume can be some orders of magnitudelarger than those (10⁻⁹ cm³ at 400-500 GPa) in diamond anvil cells whichenable the generation of static ultrahigh pressure. Ultrahigh pressurescan be generated by incident laser intensity some orders of magnitudeless than in the conventional dynamic methods using high-power pulsedlasers. Thus the present invention provides a means for exploringsyntheses of new materials with novel physical and chemical propertiesand properties of unknown substance which have been impossible ofexecution until now.

In accordance with the invention, there is provided a method capable ofgenerating ultra-high pressures which have not been achieved so far, inwhich if only a small light energy enough to heat the pressure sourcematerial up to a high temperature required to disrupt its atomic bondsis supplied, ultrahigh pressures can be generated and moreover ultrahighpressures generated in the volume-constrained space are exceptionallyhigh because extremely large expansive forces occurring from thepressure source material against its very strong bonding forces areextremely large.

In accordance with the invention, there is provided a method ofgenerating ultrahigh pressure, in which since the light energy can beefficiently supplied to the pressure source material and can be wellcontrolled by changing the intensity and the duration of the suppliedpulsed laser using the existing pulsed laser equipment which can emitlaser lights having a wavelength suitable for heating the pressuresource material, the duration of generated ultrahigh pressure can beconsiderably long compared to the conventional dynamic methods.

In accordance with the invention, there is provided a method forgenerating ultra-high pressure, in which as the optically transparentmaterial is penetrable to the externally supplied light energy, itstemperature hardly rises due to energy absorption and thermal stresshardly occurs. Therefore, the higher pressure can be obtained byapplying the larger light energy to the pressure source material.

In accordance with the invention, there is provided a method capable ofgenerating ultrahigh pressure in much lager pressure chamber than in theconventional ultrahigh pressure methods using diamond anvil cells, inwhich since sapphire has high transmittance compared with diamond and alarge single crystal of synthetic sapphire is available at a low price,it is suitable for the material forming the pressure chamber.

In accordance with the invention, there is provided a a method capableof generating controlled ultrahigh pressure according to a sample, inwhich since the pressure source material is composed of a mixture ofmaterials having large adsorption coefficient or strong bonds which haslarge absorption coefficient and strong atomic bonds as a whole so thatconsiderably large expansive forces can be obtained even if the suppliedenergy is relatively small, the peak and the duration of the generatedpressure can be controlled by combining materials.

In accordance with the invention, there is provided a method forgenerating ultra-high pressure that enables the control of temperaturein the sample by changing temperature gradients across the pressuresource material, in which since the pressure source material can bechosen among materials which have covalent, metallic, and hydrogen bondsaccording to need, the pressure source material can be adjustedaccording to the sample by combining materials that have different lightabsorption coefficients or various thermal conductivities.

In accordance with the invention, there is provided a method forgenerating ultrahigh pressure with high energy-efficiency by using thepressure source material composed of only graphite.

In accordance with the invention, there is provided a method forgenerating ultra-high pressure which enables the generation of peakpressure higher than in the case of using graphite singly as thepressure source material.

In accordance with the invention, there is provided a method forgenerating ultra-high pressure that enables the generation of higherpressure with higher power lasers, in which since the minimum diameterof the laser beam is not formed within the optically transparentmaterial, the most condensed place of the pulsed laser light does notexist in the interior of the optically transparent material, and thelocal temperature increase in the optically transparent material can beavoided thereby.

In accordance with the invention, there is provided a method forgenerating ultra-high pressure, that enables the generation of ultrahighpressure in the lager pressure chamber, with the longer duration, and bysome orders of magnitude smaller amounts of energy compared to theconventional methods, in which if only a small light energy enough toheat the pressure source material up to a high temperature or above theboiling point thereof required for inducing the disruption of atomicbonds is supplied, ultrahigh pressures can be generated and furthermoreultrahigh pressures generated in the volume-constrained space areexceptionally high because of extremely large expansive forces occurringfrom the pressure source material disrupted against its very strongbonding forces, and ultrahigh pressures which have not been achieveduntil now can be generated thereby.

In accordance with the invention, there is provided a device forgenerating ultra-high pressure that enables the generation ofexceptionally high pressure in the space under volume constraint, inwhich if only a small light energy enough to heat the pressure sourcematerial up to a high temperature required for inducing the disruptionof its atomic bonds is supplied, ultrahigh pressures can be generatedand ultrahigh pressures generated in the volume-constrained space areexceptionally high because of extremely large expanding forces occurringfrom the pressure source material disrupted against its very strongbonding forces.

In accordance with the invention, there is provided a device forgenerating ultrahigh pressure with the longer duration compared to theconventional dynamic methods in addition to the effect of the inventionin claim 11, in which the light energy can be efficiently supplied tothe pressure source material by controlling the intensity and theduration of pulsed laser by using the existing pulsed laser equipmentwhich can emit the laser light having a wavelength suitable for heatingthe pressure source material.

In accordance with the invention, there is provided a device forgenerating ultra-high pressures, in which since the minimum diameter ofthe laser beam is not formed within the optically transparent material,higher-power-pulsed laser can be used for the high-pressure generationwithout damaging the optically transparent material.

In accordance with the invention, there is provided a device forgenerating ultra-high pressure in which since larger expansion occurs inthe space compared to the irradiation in one direction, higher pressurecan be achieved.

In accordance with the invention, there is provided a device forgenerating ultra-high pressure, which enables the measurement ofgenerated ultrahigh pressures to know how generated pressures arechanged by the use of various pressure source materials or by the way ofsupplying light energy.

In accordance with the invention, there is provided a device forgenerating ultra-high pressure, which enables the measurement oftemperature in the space to know how temperatures in the space duringthe disruption of atomic bonds in the pressure source material arechanged by the use of various pressure source materials or by the way ofsupplying light energy.

1. A method for generating high pressure comprising the steps of: loading a pressure source material under volume constraint in a space partly surrounded by an optically transparent material; externally supplying optical energy of a pulsed laser beam having a predetermined energy and duration to said pressure source material through said optically transparent material; heating said pressure source material above the boiling point thereof and generating high pressure of at least 400 GPa within said space using expansive force of said high pressure source material.
 2. A device for generating high pressure comprising: a pressure source material under volume constraint in a space partly surrounded by an optically transparent material; and light energy supplying means for externally supplying optical energy of a pulsed laser beam having a predetermined energy and duration to said pressure source material through said optically transparent material so that said pressure source material is heated above the boiling point thereof and high pressure of at least 400 GPa is generated within said space using expansive force of said high pressure source material. 